CURRENT Essentials of Critical Care.pdf

Chapter 5 Fluids, Electrolytes, & Acid-Base 59■■■HypernatremiaEssentials of Diagnosis• Serum sodium [Na ] 145 mEq/L associated with hypertonicity• Altered mentation, impaired cognition, loss of consciousness• Thirst present if mentation preserved• Polyuria suggests diabetes insipidus• Elderly living in chronic care facilities with dementia and decreasedaccess to water constitute highly susceptible group• Free water deficit: depletion of total body water (TBW) relativeto total body solute• Evaluate urine osmolality, serum osmolality, responsiveness toantidiuretic hormone administrationDifferential Diagnosis• Inadequate water intake: decreased access to water, impairedthirst response• Excessive nonrenal hypotonic water loss: vomiting, diarrhea,sweating• Water diuresis: diabetes insipidus (central or nephrogenic)• Exogenous solute administration: hypertonic saline, sodium bicarbonate,glucose, mannitol, feeding solutionsTreatment• Estimate free water deficit: TBW patient [([Na ] patient [Na ] normal )/[Na ] normal ]• Rate of correction depends on acuity of onset of hypernatremia;in general, recommended to be 10 mEq/L per day• Excessively rapid replacement of free water may lead to cerebraledema• Volume resuscitation with normal saline• Once euvolemic, correction of hypernatremia changed to hypotonicfluid replacement• Addressing underlying etiology necessary as some causes requirespecific intervention; central diabetes insipidus treatedwith desmopressin acetate■ PearlThe presence of polyuria with dilute urine in the face of hypernatremiasuggests that excessive water loss is due to the inability to concentrateurine appropriately and is consistent with central or nephrogenicdiabetes insipidus.ReferenceKang SK et al: Pathogenesis and treatment of hypernatremia. Nephron2002;92:14. [PMID: 12401933]